The present invention relates to an optical fiber cable, to a method of manufacturing the optical fiber cable, and to an installation for implementing the method.
Optical fiber cables, referred to below as optical cables, can present various types of structure.
Thus, in one such type of structure commonly referred to under the trade name FLEXTUBE (copyright), the optical cable comprises opticalfiber-receiving tubes of synthetic material that are assembled together helically or in an SZ lay. The tube assembly is covered in a sheath defined by a wall having filamentary carriers embedded therein. In structures of that type, the relatively fine and flexible opticalfiber-containing tubes surround the optical fibers they contain sufficiently tightly to prevent practically any relative displacement between the optical fibers and the tubes which contain them.
In most cases, in an optical fiber network, optical cables are themselves housed in conduits, generally made of extruded synthetic material. To thread an optical fiber cable in a conduit, various known methods are known, in particular the blow method and the carry method. While such methods are being performed, the cable components are subjected to varying amounts of lengthening, the cable sheath tending to lengthen more than the optical fibers of the cable. Differences in lengthening can damage the optical fibers since the capacity of fibers for stretching is much less than that of the synthetic material sheath.
An object of the invention is to remedy that drawback by proposing an optical cable that is capable of lengthening considerably, particularly while it is being installed in an optical fiber network, but without that damaging the optical fibers.
To this end, the invention provides an optical fiber cable of the type comprising at least one tube in which optical fibers are received, the cable being characterized in that the optical fibers extend longitudinally and helically within the tube.
According to another characteristic of the cable, the tube presents longitudinal twisting.
The invention also provides a method of manufacturing an optical fiber cable as defined above, the method being of the type in which the tube provided with the optical fibers is fed to a die for manufacturing the cable from a storage reel on which it is wound, the method being characterized in that the tube is fed to the die for manufacturing the cable by unreeling the tube from the reel while the reel is held stationary, thereby imparting longitudinal twisting to the tube causing the optical fibers it contains to follow a helical path of pitch substantially equal to the length of one turn of the tube wound on the reel.
The invention also provides an installation for implementing the above-defined method, characterized in that it includes means for holding the reel in a fixed position and means for unreeling the tube carried by the reel.
Various embodiments of the installation have the following characteristics:
the installation comprises means for holding the storage reel stationary and means for unreeling the tube carried by the storage reel;
the tube is wound on the storage reel about an axis referred to as the axis of the storage reel, the means for unreeling the tube comprising guide means mounted to rotate about an axis that coincides substantially with the axis of the storage reel;
the guide means comprise a moving disk mounted to rotate about the axis of the storage reel, at one end of the storage reel, so as to form a rotary cheek for the storage reel, the tube bearing against the peripheral edge of the moving disk;
the installation comprises a stationary disk provided with an axis of symmetry that coincides substantially with the axis of the storage reel, and friction means arranged on the peripheral edge of the stationary disk to co-operate with a portion of the tube extending downstream from the moving disk in the unreeling direction of said tube in order to brake rotation of the moving disk;
the friction means comprise radial fibers or bristles;
the guide means comprise an unreeling disk mounted to rotate about an axis that coincides substantially with the axis of the storage reel and carrying an unreeling arm extending longitudinally substantially parallel to the axis of the storage reel, the arm being regularly offset relative to the axis of said storage reel so that the unreeling arm turns about the storage reel;
a guide cylinder is mounted to rotate on the unreeling arm, the tube bearing against the peripheral surface of the guide cylinder; and
the unreeling disk carries means for deflecting the tube from the unreeling arm towards an orifice for passing the tube through the unreeling disk, this through orifice being substantially in alignment with the axis of the storage reel.